Epitaxial growth technique is conventionally used to produce a semiconductor device such as a power device (e.g., IGBT (Insulated Gate Bipolar Transistor)) requiring a relatively-thick crystalline film.
In the case of vapor phase epitaxy used in epitaxial growth technique, a wafer is placed inside a film-forming chamber maintained at atmospheric pressure or a reduced pressure, and a reaction gas is supplied into the film-forming chamber while the wafer is heated. As a result, a pyrolytic reaction or a hydrogen reduction reaction of the reaction gas occurs on the surface of the wafer so that an epitaxial film is formed on the wafer.
In order to produce a thick epitaxial film in high yield, a fresh reaction gas needs to be continuously brought into contact with the surface of a uniformly-heated wafer to increase a film-forming rate. Therefore, in the case of a conventional film-forming apparatus, a film is epitaxially grown on a wafer while the wafer is rotated at a high speed (see, for example, Japanese Patent Application Laid-Open No. 2008-108983).
In recent years, attention has been given to SiC (silicon carbide) epitaxial growth technique. SiC is characterized in that its energy gap is two or three times larger and its dielectric breakdown field is about one digit larger than that of a conventional semiconductor material such as Si (silicon) or GaAs (gallium arsenide). For this reason, SiC is a semiconductor material expected to be used in high-voltage power semiconductor devices.
In order to obtain a single-crystalline SiC thin film by epitaxial growth of such SiC, the temperature of a substrate needs to be increased to 1500° C. or higher. Therefore, a susceptor on which a wafer is to be placed is made of high heat-resistance material. A specific example of such a susceptor includes one obtained by coating the surface of a base material made of graphite with SiC by CVD (Chemical Vapor Deposition) (see, for example, Japanese Patent Application Laid Open No. 2004-75493).
Meanwhile, when epitaxial growth of SiC film is performed in a film-forming chamber, a SiC film is deposited not only on the surface of a wafer but also on a susceptor. If this film comes off, dust is generated thereby causing a defective epitaxial film to be formed on the wafer. For this reason, the deposited film needs to be removed.
A SiC film deposited on a susceptor during the SiC film formation process can be removed by an etching process. The end of cleaning is conventionally controlled by the thickness of a SiC film formed in the SiC film formation process and the length of etching time. However, when the end of cleaning is controlled in such a manner, it is difficult to determine whether the SiC film deposited on the susceptor has been reliably removed or not. Therefore, cleaning is conventionally performed for a longer time than calculated.
However, such a method wastes time on unnecessary cleaning, and further there is also a fear that a SiC coating film constituting the susceptor is also damaged.
Japanese Patent Application Laid Open No. 9-78267 proposes a method for monitoring the end point of cleaning. According to this method, an absorbent container containing an absorbent is provided in an exhaust system of a film-forming apparatus, and an exhaust gas is introduced into the absorbent container and a change in the temperature in the absorbent container is measured to monitor the end point of cleaning. However, this method has a problem that a change in the temperature in the absorbent container cannot be accurately detected due to degradation of the absorbent.
In view of the above problems, it is an object of the present invention to provide a semiconductor substrate manufacturing apparatus that makes it possible to remove a film deposited on a susceptor during SiC epitaxial growth and to enhance manufacturing yield.
Other challenges and advantages of the present invention are apparent from the following description.